1. Field of the Invention
This invention relates to multiplexing information channels to a single channel, and more particularly to multiplexing data channels to a single channel prior to overhead extraction and insertion.
2. Description of Related Art
In telecommunications protocols, data is typically framed or packetized prior to transmission. In each of these frames or packets, there will be a section containing overhead or header information, and a section that contains data. Overhead or header information typically includes information for routing a transmission, among other types of information.
Referring to FIG. 1, there is shown a block diagram of an exemplary embodiment of Synchronous Transport Signal (STS) frame 10 in accordance with the prior art. STS frame 10 may be any of a variety of levels, conventionally where N is equal to 1, 3, 12, 48, 192, or 768 and data rate is N times 51.84 megabits per second (Mbps); although, N may be an integer coventionally from 1 to 768. As shown in FIG. 1, an STS-3 frame 10 is indicated. Frame 10 comprises section overhead (SOH) 18, line overhead (LOH) 19, and in payload area 12 comprise path overhead (POH) 15 and user data area 14 both of synchronous payload envelope (SPE) 13. STS-3 frame 10 may be provided on a separate channels. So, continuing the above example, STS-N may be channelized.
In multi-channel physical layer devices, individual pins associated with each field in each individual channel header are conventionally provided. Other multi-channel physical layer devices have distinct pins for all header information for each channel. Accordingly, depending on the number of channels as well as complexity of a protocol employed, each type of the physical layer devices mentioned above result in a device with significantly large number for a pin count as N is increased. It should be appreciated that this pin count is conventionally doubled owing having both a transmit path and a receive path. Conventionally, both paths have the same number of pins associated with overhead bytes for their respective data path.
Because data rate may vary slightly from one STS channel to the next STS channel, absence of alignment of data causes problems with respect to extracting overhead. One signal may be at 51.84 megabits per second while another data rate on another channel is slightly higher and yet another data rate on yet another channel is slightly lower than that data transmission rate. Accordingly, overhead from such signals is extracted and inserted separately for each data rate-varying channel. In other words, there is an independent extraction port and an independent insertion port for each channel. This, however, uses a substantial number of pins.
Accordingly, it would be desirable to provide an interface with a lower pin count, and more particularly to reduce pin count on both transmit and receive sides.